Caption: Heart-lung machine. Theatre assistant notes the reading of a heart-lung machine during heart surgery. The machine takes over the function of the heart and lungs, giving the surgeon more time to operate and preventing blood from obscuring the operation site. The machine bypasses the patient's heart and lungs, allowing the heart to be stopped. Deoxygenated blood is taken from the heart, and pumped through an oxygenator which adds oxygen and removes carbon dioxide. The oxygenated blood passes through a heat exchanger to give the blood the desired temperature. It is then pumped back into the body.